Blank page on reader.

When trying to read a book, I get a blank page. Output shows the following error:

```
flutter: failure to decode theme: Null check operator used on a null value
flutter: null
```

This is on linux (Arch Linux), flutter engine version 3.13.6

There is also an issue with permissions on linux, the permission handler plugin doesn't support it but I made a simple package that assume all permissions are granted to work around it.